Companies have been making iPhone accessories for three years now, so it's somewhat telling that -- at least for now -- no major manufacturer has stepped up to the task of developing a slide- or swivel-out keyboard accessory for an iPhone. While the necessary Bluetooth and keyboard software support was added to iOS only months ago, there's little doubt in our minds that designers were sketching out keyboards as soon as the original iPhone was announced, and though the increasingly controlling Apple may have quietly put the kibosh on earlier options, the floodgates are open now. Yet only two companies, both all but unknown in the iPhone accessory market, have actually marketed pocket-sized keyboards to iOS users: Pyramid Distribution with its ProMini, and now ThinkGeek with the TK-421 Mobile Keyboard Case ($50).

For sure, TK-421 has a few major advantages over ProMini. starting with a $20 lower price tag, continuing with larger Chiclet-style keys that are physically separate from one another, and ending with a design that not only fits directly into the iPhone 4’s footprint, but actually encases the phone while swiveling out from underneath it. TK-421 nearly doubles the iPhone’s thickness, but it’s much smaller than ProMini and dispenses with most of the unnecessary features Pyramid included, such as a trackpad for use with computers, and a laser pointer that added nothing to the product. ThinkGeek’s keyboard rotates open with a satisfying click and closes using a magnet, the latter feature somewhat impacting the device’s compass. Unlike ProMini, TK-421 isn’t device-agnostic: the model we tested works only with the iPhone 4, while a separate version is made to fit the iPhone 3GS. If you’re a frequent device upgrader, this mightn’t be the keyboard for you.

Before discussing the unit’s other and potentially more serious issues, it’s worth mentioning that this accessory works pretty much as expected when it’s working. You get a full QWERTY keyboard to tap on, each key clicking reassuringly as you depress it, and there’s a function key to let you access secondary key features such as navigation arrows, volume controls, and play/pause/track buttons. While using the keyboard requires relearning of key positions such as shift, control, and enter, all of which are not only small but moved downwards from where they would be found on larger input devices, it’s eventually possible to become familiar enough with the key layout to compose real—though imperfect—text on the iPhone’s screen. Given the choice to cram more keys into a smaller space or use keys that are right-sized for big fingers, ThinkGeek chose the latter route, and some users will be better off for that decision. The unit also feels respectably built, rather than flimsy; the matte black plastic shell will likely stand up reasonably well to normal use, while we’d only worry about the swiveling hinge in situations of abuse. In other words, open the keyboard when you need it, close it when you don’t, and it should be fine.

The issues with TK-421 are, however, non-trivial. Start with the case, which was clearly not designed by a company familiar with the problems of iPhone cases in general or the iPhone 4 in specific: it’s a slider design with uncomfortably tailored button holes that make simple volume and Sleep/Wake depression more difficult, and use of the headphone port a problem for anything save Apple-thin connectors. It even blocks the top noise-canceling microphone hole entirely. While TK-421 does work in docks, and provides fine access to the bottom speaker and microphone, you’ll need to swivel the keyboard out, first; some accessories may require the removal of its bottom piece, too. To be clear, this isn’t a bad case, but it will unnecessarily cause a number of problems for different types of users.

Though its importance will vary from user to user, one of TK-421’s issues strikes us as impossible to ignore in a device-specific keyboard: the fact that its function keys weren’t optimized for the iPhone 4, or more broadly, iOS. The presence of a Mac-like Expose function key is odd enough, but then there’s an IME key, a print screen key, brightness keys, and menu and home keys, none of which work. PC- or Mac-ready keyboards such as Pyramid’s ProMini can get away with some of this incompatibility on the grounds that other devices may be able to use these features, but when a keyboard’s made for the iPhone specifically and yet doesn’t offer full access to its own suite of keys, and includes some that don’t work properly when they should, that’s a problem. At least, it will be for certain users; others mightn’t mind.

ThinkGeek’s battery management implementation has some compromises, too. On one hand, initial pairing was easy, and once you learn the re-pairing trick—just hit a key—resuming use of the keyboard when it has automatically powered itself down isn’t that difficult. As TK-421 turns off after several minutes to conserve battery life, you may find yourself doing this often. TK-421 includes a micro-USB to USB cable for recharging and uses an internal battery that has no stated longevity but should last most users for weeks between charges. On the other hand, TK-421’s use of a stiff, recessed power switch and a thin pairing button lead to a little more frustration than better-designed power and pairing controls would have. Accidentally tap the pairing button and you’ll need to go through the pairing process with your iPhone again manually, even if you turn the keyboard off and on again. Actually turning the keyboard on and off required us to use a nail rather than a fingertip. These issues aren’t fatal, but they’re annoyances nonetheless, and we experienced them a few times during testing.

As iPhone accessories go, TK-421 is the rare product that we’ve literally been waiting to use for years, but ultimately felt less than totally enthusiastic about during testing. We view it as more of a proof of concept than a completely finished product, coming far enough that ThinkGeek clearly has accomplished a significant milestone just by bringing it to market, but not to the point where we’d actually want to keep it on an iPhone and actually use it on a daily basis for typing. At this point, we’d hold off for a more polished sequel or alternative, but if you’re dying for an easily carried physical keyboard and willing to adapt to TK-421’s idiosyncrasies, the price is certainly right, and it does generally what it’s supposed to do. It’s worthy of our limited recommendation, which is to say that’s it’s not yet ready for prime time, but a niche of accommodating users such as early adopters may find its functionality sufficient to merit the purchase.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.